The present invention relates generally to vaporizing type combustors, for use in gas turbines, as differentiated from an atomizing type. When functioning properly, a vaporizing type combustor normally tends to operate with less soot generation than do the atomizing types. In attempting to prevent premature plugging of heat exchangers for such apparatus, it has been found desirable to use the vaporizing type of combustors, especially in gas turbines which use either regenerators or recuperators.
Vaporizing type combustors previously have used fuel vaporizing tubes, and known types have included a so called "candy cane type" or a so called "T-type," the "T-type" being a double armed candy cane type. Examples of such vaporizing tubes are found in the prior art, including, but not limited to, U.S. Pat. No. 3,757,522 which discloses a T-type vaporizer tube; British Pat. No. 1,253,471 which also discloses a T-shape; and additional examples are disclosed in U.S. Pat. No. 4,030,288, the latter patent being owned by a common assignee with the present application; and U.S. Pat. No. 3,913,318. Other similar structures have heretofore been used.
Problems exist with such vaporizing tubes however, including, for example, a burning out of portions of the vaporizer tube due to localized high temperatures or hot spots; burning out or thermal fatiguing of head plates or splash plates, if the latter is used. Additionally carbon may form in various parts of the vapor tube per se, if such parts are too cool in operation, or on parts of the head plates or splash plates. Under such circumstances, if conditions change, the built up carbon may break away and cause erosion; or localized hot spots may form if such carbon begins to burn; or flow may become adversely affected by being impeded; or the carbon may act as an insulator and thus increase the severity of thermal stresses in various parts.
In a significant percentage of prior known and used vaporizing tubes of the candy can type, there is a full reversal of the flow direction, with the discharge of the vapor being in a direction opposite to the flow into the vapor tube. The flow turns in such prior art apparatus have in some instances been purposely made sharp, as by use of mitered joints and the like, in order to create eddies and a purported better mixing of vapor with the air. This type of construction and resulting operation, however, have been found to be undersirable in that such eddies tend to increase residence time of the fuel and air mixture at certain locations, and if ignition occurs within the tube, for example, a local hot spot can be rapidly formed, which can lead to a burn out or local melting.
Basically the present invention has as a partial object a vaporizing tube for use in vaporizing type combustors, with the tube having structure and design which serve to maintain more uniform temperatures in the vaporizing tube, as well as in a splash plate, if used, or the head plate. Additionally, the design is such as to eliminate, in so far as possible, carbon build-up within the vapor tube itself, or on other areas of the apparatus, and generally to eliminate existent defects and drawbacks of the prior art.